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Date: Thu, 15 May 2025 18:03:46 +0000
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Subject: Re: [RFC PATCH v2 00/51] 1G page support for guest_memfd

On Wed, 2025-05-14 at 16:41 -0700, Ackerley Tng wrote:
> Hello,
> 
> This patchset builds upon discussion at LPC 2024 and many guest_memfd
> upstream calls to provide 1G page support for guest_memfd by taking
> pages from HugeTLB.

Do you have any more concrete numbers on benefits of 1GB huge pages for
guestmemfd/coco VMs? I saw in the LPC talk it has the benefits as:
- Increase TLB hit rate and reduce page walks on TLB miss
- Improved IO performance
- Memory savings of ~1.6% from HugeTLB Vmemmap Optimization (HVO)
- Bring guest_memfd to parity with existing VMs that use HugeTLB pages for
backing memory

Do you know how often the 1GB TDP mappings get shattered by shared pages?

Thinking from the TDX perspective, we might have bigger fish to fry than 1.6%
memory savings (for example dynamic PAMT), and the rest of the benefits don't
have numbers. How much are we getting for all the complexity, over say buddy
allocated 2MB pages?

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